The present invention is generally concerned with drive mechanisms for operating rotary structures, and more particularly with an improved drive system for intermittently operating rotary structures.
As shown in U.S. Pat. No. 2,934,009, issued Apr. 26, 1962, Bach, et al. and assigned to the assignee of the present invention, there is described a mailing machine which includes a postage meter and a base on which the postage meter is removably mounted. The postage meter includes a rotary printing drum and a drive gear therefor which are mounted on a common shaft and normally located in a home position. The base includes a drive mechanism having an output gear which is disposed in meshing engagement with the drum drive gear when the postage meter is mounted on the base. The drive mechanism includes a single revolution clutch, having a helical spring, for rotating the drum from the home position and into engagement with a letter fed to the drum. Each revolution of the clutch, and thus of the drum, is initiated by a letter engaging a trip lever to release the helical spring. In the course of each drum revolution, the drum prints a postage value on the letter while feeding the same downstream beneath the drum as the drum returns to its home position. Thus the drive mechanism intermittently operates the rotary printing drum.
Although the single revolution clutch structure has served as the workhorse of the mailing machine industry for many years, it has long been recognized that it is a complex mechanism which is relatively expensive to construct and maintain, tends to be unreliable in high volume applications, and is noisy and thus irritating to customers.
Accordingly, an object of the invention is to replace the drive mechanism of the prior art with a simplified, highly reliable and quietly operating drive system including a rotary timing cam.